Radar system operational training system



Aug. 5, 1952 E. M. JONES RADAR SYSTEM OPERATIONAL TRAINING SYSTEM medApril 3o, 194e 2 Sl-IEETS-SHEET l Aug. 5, 1952 E. M. JONES RADAR SYSTEMOPERATIONAL TRAINING SYSTEM 2 SHEETS-SHEET 2 Filed April 30, 1946VVE/V701? EDWARD M. JONES T TOR/VE Y Patented Aug. 5, 1952 STATE EdwardM. Jones, Hanover, N. H., assignor, by

`mesne ,assignments, Yto the United States of America as represented bythe Secretary of War Applioaiibnliprilso,194e, serial No. 666,022

. 1` This invention relates to radar training equipment and particularlyto means for simulating realistically incoming radar signals.

It has beenfound desirable in developing radar circuit' through leads Iand 2 connected to an inverter video section 3 having a double triode 5of the 6SN7-GT type.' In tube 5 two independent signals'may be mixedwhile the video sigoperations to usetraining sets into which are 5 nalis amplified and inverted.' In some cases a introduced artificiallyproduced signals correblocking oscillator pulse from a triggergenerator, spending as closely as possible to the signals renot shown,is impressed on one of the grids Il ceived during normaloperation. Theseartiand l2 of tube 5 in'place 0f the target Signal. iiciallyproduced'or'synthetic video signals have simulating the transmittedpuise 0f a radar Setbeen fed into thevideo amplifier of the radar setThe oscillator uses tvvo Separate cilcuitS t0 receiver, which usuallyutilizes a superheterodyne DIOduce ya puiSed I-F cullent- TheiiIStOSciicircuit. The results'have been unsatisfactory, iatOIG." usinga`6AG7 type tube, iS Set t0 Operate however, because noise-is either notpresent, or at 45 mc., and is' cut off except'when a video isincorrectly combined with the signals, and the signal pulse is appliedthereto. The Second oseilgain control does 'not' function normally and15 lator 1, using a GAC? tube, operates continuously various 'otherfactors make the operation as at 75 mc. learned on thertrainerdissimilar to that ex- The outputs of oscillators 6 and 1 are appliedperienced under operating conditions. together to an ineicient mixer 8.the Output 0f The present invention provides means for con- Which willbe ithe Adifference .frequency between verting synthetic video pulsesinto proportional the two oscillators or 30^mc. This is the desired I.F.pulses. These in rturn are fed into the I.F. value for the I.F. The useof two oscillatorsl 6 amplifier of the radar set insteadof the signalsand 1 in this fashionreduces R. F. leakage from normally taken from therst detector. The apthe modulator'into the radar receiver, which wasparatus for accomplishing. this purpose, which a serious problemfinsingle oscillator trainers. will be called a modulator, permits theproper Unless veryfela'b'orateshielding measures were saturation eiectsto take place in the I.F. poremD10yed,'-30 inc-carrier leakage currentsfound tion of the radar set, and allows normal operation their Way finto:the "receiver,Y which tended to by the trainee oi' the gain control,which is an saturate, S0 that the Signals Could not be Seen.'importantelement in training'for the operation Due t0 the band DaSSlimits 0f the receiver. of equipment of this type. It provides theproper 30 mc. |5 mc., neither the-7 5 mc. nor the 45 mc. noiseinterference, for the trainee must become currents can Produce thiseiiect- Further, Since accustomed to identifying signals during thepresthe 45 mc- Oscillator iS pulsed. the 30 mcdifenee of inter-ference,a part of which is noise proference frequency will be developed onlyduring duced inthe'receiver itself. Grain control is also receptionOfthe Video Signals, which is a very provided by means of which theinstructor can small fraction of the time. Hence ordinary R.F. vary thesignal strengthat will, including its reshielding mayl be employed. Aconventional duction to a value rwell below the Ynoise level. rangeattenuationgate circuit, not shown, sup- The invention has beenillustrated 4in the plies the rangevgate bias to the mixer 8 throughdrawing, in which: lead 9'. i e g y Fig. 1 is a block diagram of atraining unit 40 Simulation of noise normally developed Withinincorporating the invention; and the radar set, particularly in thepre-amplier Fig. 2 is a schematic circuit diagram of the stages, isaccomplished through the use of a training unit. noise generator lllusing a 6AC7 type tube, the The basic elements to accomplish the objectsoutput of which is mixed with the attenuated I.F. explained above are anoscillator to produce the in a separate mixer and pre-amplier tube Il ofI.F. current, switching circuit to modulate the the same type. syntheticvideo pulses onto the I.F. current, and If it is desired to simulatefading, a convenan attenuator. Certain other elements are tionallyobtained varying bias control voltage, deadded as described hereafter toaccomplish additails of which are omitted from Fig. 2, may be aptionalfunctions. The elements are shown gen- 5o plied to one or both grids ofthe double triode 5 erally in the block diagram of Fig. 1 and corin thevideo inverter component 3, as indicated respondingly numbered arrowsare used in Fig. 2 schematically in Fig. 1 at l2. to indicate roughlythe extent of the circuit ele- Returning to the pulsed 4.5 mc.oscillator 6: the ments shown in blocks in Fig. 1. functioning of thisHartley oscillator circuit is The synthetic video signals are applied tothe controlled by a switch tube circuit I4. The tank ceases to flowtherethrough, the cathode imped-v ance increases, and hence 45 mc.oscillations begin to lbuild up in the Hartley circuit 6.

The 45 mc. pulsed oscillator. circuit 6 is stabilized by the switch tubecircuit'IlI, since when the cathode I9 swings as negative as the gridI1, current will again ow through Ythe tube I6. Enough energy will thusbe absorbed to prevent further increase in the amplitude of theoscillations. A small portion of the 45 me;l oscillations is fed from aplate load resistor 20 to a grid 29 of tube 22 of the mixer circuit 8.This grid 29 is biased to ground potential by means of a small resistor24, which alsofltersout any video frequency inthe plate circuit ofoscillator 6.-

The output of 75 mc. local oscillator circuit using a 6AC7 type tube istaken from the grid K end of the plate-grid inductance 25 and coupled tocontrol grid 26 of the mixer tube.22 through acoupling capacitor 21. i

The mixer circuit 8 operates as an I.F. amplier and has three inputs.The 45 mc. output of thepulsed oscillator 9 is applied tothe third grid29 of the 6117 type tube. The 75 mc. output from .the local oscillatorcircuit .'I is applied-to the contril grid 26,` which also receives vtheattenuation with range, gate, voltage received from the trigger unit(not shown) through lead Sas stated above.

The output vof the mixer tube 22 is loosely coupled to the controlgrid3| Oi-pre-amplier stage tube II (second I.F. stage) through a capacitor32 having a value of substantially lmicro-microfarad and alf-larger`capacitor 34.

Capacitance 3 2 attenuatesthe 30 mc. output of the mixerfcircuit 8 so`that .it may be mixed with the output or" thernoise generating circuitI0. The noise-across a 1.5K gridlresistor 35 is amplifiedwitlifaband'width 'of 2.4 mc.xby the noise generator' tube31,' vand isthen able to cover. such 30 mc. pulses-as leak through to the outputwhen the mixer 22 is biased off and to minimize the effect of pickup 'ofexternal 30 mc. signals by the cable joining the modulator to the radarreceiver.l l g This modulator Vmay also be usedwith moving targetindicator training. Fixed echo signals, already at -L-F., generated inasupersonic trainer, are applied to the control grid 3S of the noisegenerator tube'31, while the movingtarget echoes are received in theusual manner.

It will be recognized that the types of tubes andthe various circuitconstants specified are subject to change as desired, and that otherengineering changes in the circuit may be made within the scope of `theinvention. The trainer as described makes possible the effectivetraining of radar operators by simulating with greater accuracy thanheretofore possible the conditions of reception which will beexperienced in the iield by the trainee.

What is claimed is:

A training device lfor a pulse echo -type radio obstacle detectionsystem having a superheterodyne receiver, comprising a rst normallyinoperative oscillator circuit having a given characteristicfirstfrequency, a second oscillator having ach'aract'eri'sticl secondfrequency diering yfrom said first frequency by the intermediatefrequency of said system, a mixer stage coupled to both ofsaidoscillators for combining the signal frequencies thereof and to producea signal wave having the saidintermediate frequency; an electronicswitch circuit for-controlling the operation of said first oscillatorincluding a tube and an `impedance incircuittherewith, said impedanceforming a part of saidV first oscillator circuit and having avaluevarying in response tor the current therethrough, a signal transducerconnected to said controlling circuit and having a connecting' means toa source of detection-systern-simulating,-sign'alv pulses forapplication of said pulses-thereto, whereby said first oscillatorbecomes operative; ran .amplifierv rfor translating the pulse`signalsirom said mixer stage con-v nectedthereto; means 'for supplying anoise signal connected to vsaid translating amplifier, and meansforapplying a signal amplitude controlling voltagel to saidtransducerfor lcontrol of the pulse amplitudes therein. 1

n L l`lIi}D'\'v/'Al:tD M. JONES.

f f' REFERENCES CITED The followingrefer'ences are of record in the fileof this patent; Y Y

UNrrnn srArEs lPA'rErrrs 516,942; publishedAugust-fl, 1949;v iiledJanuary

